[–] Citron 1 point 0 points 1 point (+1|-1) ago
It depends. My mother tongue is Arabic but I'm a fluent speaker of English and French. Most of the time I think in Arabic. However sometimes I'm playing games IRL, I think like everyone else. When for instance you're navigating a new premise, or imagining a scenario, that's when I switch to whichever language represents the character I'm imagining myself. I don't know if it makes sense.
[–] bugmenot 2 points 1 point 3 points (+3|-2) ago
From the other comments, and my own experience, it seems that most people tend to think in the language they use most on a daily basis. That is, if they are fluent enough in those other languages. The same goes for dreams.